A COMPARISON OF STANDARDIZED METHODS FOR PREDICTING THE HAZARDS OF WHOLE-BODY VIBRATION AND REPEATED SHOCKS

Methods of measuring, evaluating and assessing whole-body vibration and repeated shock are offered in ISO 2631 (1974, 1985), BS 6841 (1987), and ISO 2631 (1997). This paper presents a comparison of guidance on the health effects of vibration and repeated shock given in these standards. International Standard 2631 (1974,1985) offered a set of exposure limits. British Standard 6841 (1987) defines a measurement and evaluation procedure (based on frequency weightings and the vibration dose value, VDV), gives an action level that can be used to assess vibration severity, and mentions some appropriate actions (consideration of the fitness of exposed persons, design of safety precautions, regular health checks). International Standard 2631 (1997) is unclear in several important areas: which body postures and axes are to be assessed; whether evaluations of multi-axis vibration should be based on the “worst axis” or a combination of the frequency-weighted acceleration in all axes; why a new frequency weighting,Wk, is proposed for vertical vibration when it is almost within the error tolerance of an existing weighting,Wb; why a 1·4 multiplying factor is used to evaluate vibration with respect to health but not with respect to comfort; how to choose between different time-dependencies (overall r.m.s.,VDV, running r.m.s., and no-time-dependency); allowing use of either the maximum value of a running r.m.s. (i.e.,MTVV) or theVDV; allowing different averaging periods when calculating theMTVV; using the crest factor to choose between r.m.s. and either theVDVorMTVVmethods; defining two inconsistent criteria for deciding whether to use either theVDVorMTVVmethods; giving no guidance on howMTVVvalues should be assessed; including two very different “health guidance caution zones” (for interpreting r.m.s. andVDVmeasures); providing ambiguous wording for the health guidance caution zones. Very different conclusions can be reached according to what is measured, how the vibration is evaluated and how it is assessed according to ISO 2631 (197). However, even though it employs a slightly different frequency weighting for vertical vibration, and a 1·4 multiplying factor for horizontal vibration, ISO 2631 (1997) can be interpreted so as to provide evaluations similar to those made according to BS 6841 (1987). It is concluded that the recently revised International Standard for measuring, evaluating and assessing human exposures to vibration and shock will cause unnecessary confusion.